1. Field of the Invention
The present invention relates to distortion circuits, and more particularly, to distortion circuits capable of imparting distortion effects to audio data such as a musical tone data.
2. Background Art
A distortion circuit imparting distortion effects to a digital audio data of a digital circuit, for example as shown in FIG. 7, which is comprised of a non-liner table 1 having the input/output characteristics shown as the curve b in FIG. 8, or comprised of an amplifying multiplier 2 multiplying an input data by an amplifying coefficient, and an attenuating multiplier 3 multiplying the multiplied result of the amplifying multiplier 2 by an attenuating coefficient as shown in FIG. 9.
When the sine wave data shown as the curve a in FIG. 8 is supplied to the non-liner table 1 shown in FIG. 7, output data on which is represented by a broken line of the curve c in FIG. 8 are distorted, and is output from the non-liner table 1. In contrast, when the sine wave data shown as the curve a in FIG. 10 is supplied to the amplifying multiplier 2 shown in FIG. 9, the sine wave data is multiplied by an amplifying coefficient of the amplifying multiplier 2. As a result, the part where an amplitude level is large among the parts of the multiplied result is limited by a limiter built into the amplifying multiplier 2. Then, the output data from the amplifying multiplier 2 is multiplied by the attenuating coefficient in the attenuating multiplier 3 to adjust the proper level. Accordingly, the output data wherein the waveform is distorted, is output as shown as the curve b in FIG. 10.
The amplifying multiplier 2 is composed of a multiplier 4 and a limiter 5 as shown in FIG. 11. Both an input bit width and an output bit width of the amplifying multiplier 2 is p bits (p is a positive integer). However, there is the case where the bit width of the multiplied result of the multiplier 4 becomes q bits (q is a positive integer, and p is less than q). Accordingly, when the bit width of the multiplied result of the multiplier 4 is larger than the output bit width p of the amplifying multiplier 2, the bit width of the multiplied result of the multiplier 4 is limited, by the limiter 5, to the maximum value or the minimum value of the output bit width p of the amplifying multiplier 2. For example, when the multiplied result of the multiplier 4 is a positive value and its bit width is larger than the output bit width p of the amplifying multiplier 2, the bit width of the multiplied result of the multiplier 4 is limited to the maximum value of the output bit width p of the amplifying multiplier 2 of the limiter 5. In contrast, when the multiplied result of the multiplier 4 is a negative value and its bit width is larger than the output bit width p of the amplifying multiplier 2, the bit width of the multiplied result of the multiplier 4 is limited, by the limiter 5, to the minimum value of the output bit width p of the amplifying multiplier 2.
As described above, the distortion effect is imparted to the sine wave data in the distortion circuit.
In the above-mentioned conventional distortion circuit, in the case of the distortion circuit shown in FIG. 7, there is a positive effect in that every distortion effect having every characteristic can be realized. However, there is a drawback in that memory such as a ROM having a large memory capacity is necessary and the circuit construction of the distortion circuit is complex. In contrast, in the case of the distortion circuit shown in FIG. 9, there is the positive effect in that the circuit construction is simple. However, because the distortion of the audio signal begins sharply, the musical forced distortion effect is imparted to the audio data. Accordingly, the distortion circuit shown in FIG. 9 is not suitable for using for an electronic musical instrument.